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Vitamin D is needed for growth and for the forming of bones. It controls the amount and placement of calcium and phosphorus (bone-building minerals) throughout the body. The popular name for vitamin D is "the sunshine vitamin." When your body is exposed to the ultraviolet rays of the sun, an oily substance in the skin is converted to vitamin D and subsequently transferred to the blood stream. However, according to one study, people with heavily pigmented skins may be prevented from assimilating up to 95 percent of vitamin D. It is the only vitamin that is also created in the body from another bodily substance. Vitamin D is unique in being not only a vitamin but also a hormone. Our greatest need for vitamin D is during the growth years. To assure that children, teenagers, and pregnant and breast-feeding women meet their needs, milk is fortified with 400 IUs of vitamin D per quart, equivalent to 10 micrograms of cholecalciferol. Since milk also supplies calcium and phosphorus, and contains fat to help the body utilize vitamin D, it is the ideal food to promote the development of strong, healthy bones. Children who are strict vegetarians and eat no animal protein (including milk products) are particularly prone to rickets. The end of childhood does not mean the end of our need for vitamin D. Most adults who live in moderate climates and spend part of their time outdoors can meet this need through some daily exposure to the sun. But people who are dark skinned, who spend all their time indoors, or who live in smoggy regions should be careful to get some Vitamin D from their diets. The two vitamin D-deficiency diseases are rickets which causes bone deformities in children, at osteomalacia, a condition characterized by softened bones in adults. Much of the groundwork in curing these diseases was done in England early in the 20th century. When a thick blanket of smog created by industrial pollution kept the sun from reaching the workers' tenements, the children in that area developed large joints, knock-knees, and the deformed spine that are characteristic of rickets. Regular dosages of cod-liver oil-one of the few food sources of vitamin D-subsequently prevented the condition. As with vitamin A, excess doses of vitamin D can create serious health problems. Weight loss, weakness, vomiting, and diarrhea are signs of hypervitaminosis D. Since these symptoms can be caused by other factors, it is always wise to check with your doctor. In advanced stages, toxic amounts of this vitamin can cause calcium deposits in the soft tissues such as the kidneys, eventually causing death. Amounts of vitamin D as small as 3 to 5 times the RDA are dangerous for children, while 10 times this amount is dangerous for adults. A daily intake of 10 micrograms of cholecalciferol (or 400 international units-the amount in one quart of milk) is considered safe for people of all ages. Natural sources of Vitamin D are few. It is found in egg yolk, liver, and oily fish such as tuna or herring. Fish liver oils, the richest concentrated source, are considered a supplement rather than a food. | 
